Honeywell Smart Valve 6+1 code

jbjam100

I’m using the SV9520H8042 smartvalve in a 20 year old AirFlo furnace. A few years ago noted that the system would blow cold air and the valve gave off a 6+1 code. This puts the system into a one hour timeout during which the fan runs without heat. When one hour passes, the system auto resets and warms up again. This would happen about once a week. If I was home, I could power off and back on to reset.

I called an HVAC guy and he tested and cleaned all the usual suspects and could not find it. I eventually bought and installed a new smart valve. Still happens.

Any ideas?

Thanks!